ALUMINUM-MEDIATED FOSETYL-AL EFFECTS ON PEROXIDASE SECRETED FROM GRAPEVINE CELLS

Grapevine (Vitis vinifera cv. Monastrell) suspension cell cultures wer e treated with 1.5 mM fosetyl-Al for 48 hr at 25 degrees C to test whe ther this compound, which is frequently used as a systemic fungicide f or grapevine diseases caused by oomycetes, is capable of inducing defe nse reactions in healthy non-diseased grapevine cells. The results sho wed that neither fosetyl-Al nor its degradation products in vitro, pho sphorous acid, ethanol and Al3+, are capable of inducing resveratrol s ynthesis, the production of active oxygen species or increases in pero xidase levels in the culture media. The primary mode of action of fose tyl-Al cannot, therefore, be attributed to a specific activation of na tural defense mechanisms. Fosetyl-Al, in an effect mediated by Al3+, l eads to a reduction in the level of peroxidase activity secreted to th e culture medium, this being an effect specific for certain peroxidase isoenzymes. In this context, fosetyl-Al treated cells appear to be an excellent model system for studying the factors which control peroxid ase turnover and peroxidase secretion in grapevine cells cultured in s uspension.